Learn Italian: Mio fratello ha lavorato da ingegnere per dieci anni. - My brother worked as an engineer for ten years.

When talking about acting in a certain role or profession, Italian uses the preposition da. While English says "as an engineer", Italian translates this idea using da followed directly by the profession. Using come here would sound more like a comparison, meaning "like an engineer", rather than actually being one.

Why is there no article after da? Shouldn't it be da un ingegnere?

When da is used to indicate a role, profession, or stage of life, you drop the article completely. You just say da + the noun, like da ingegnere (as an engineer) or da bambino (as a child).

Why is the past tense ha lavorato (passato prossimo) used here instead of lavorava (imperfetto) if he worked there for ten whole years?

Even though ten years is a long time, the action has a clear, stated duration (per dieci anni) and is considered a completed event. The passato prossimo is used for finished actions with a defined time frame, while the imperfetto would be used for ongoing background descriptions or habits where the start and end aren't the focus.

Just to refresh, why is it Mio fratello and not Il mio fratello?